Stress fractures of the tarsal navicular bone: CT findings in 55 cases.

OBJECTIVE: The purpose of this article is to present the CT findings in 55 cases of tarsal navicular stress fracture before and after treatment and to describe the CT protocol used. MATERIALS AND METHODS: Fifty-five navicular stress fractures in 54 patients whose initial and follow-up CT scans were available for study were retrospectively reviewed. In most cases, contiguous 1.5-mm axial and 3-mm coronal scans of the navicular bone had been obtained. Both feet were scanned for comparison. Follow-up scans were obtained between 4 weeks and 6 years. RESULTS: On review, fractures were evident in all cases, but six small fractures (11%) were missed at the initial interpretation. All fractures involved the central third of the proximal dorsal margin of the navicular bone. Fifty-three fractures (96%) were partial. Forty-three partial fractures were linear, five were linear with bone fragments, and five were rim defects with ossicles. In 13 cases (24%) the fracture was small, 10% or less of bone height. The earliest sign of healing, slight dorsal cortical bridging, was seen in three of eight cases in which follow-up was done at 6 weeks. Firm cortical union was noted in 10 (32%) of 31 by 4 months. Nonunion occurred in 12 and was indicated by the persistence of the fracture gap and lack of cortical healing. Medullary cysts (five) and cortical notching (two) were noted to persist after complete healing. CONCLUSION: CT scanning is a suitable method for detecting navicular stress fracture and for performing follow-up examinations. Small fractures may be overlooked owing to lack of familiarity with their appearance.